1. Field of the Invention
The present invention relates to a passive-type distance measuring apparatus that is provided with a distance measuring sensor which converts incident light into an analog signal.
2. Description of the Related Art
A conventional passive-type distance measuring apparatus, which is widely used as a passive-type AF system for AF cameras, divides the image viewed through a predetermined distance measuring zone (e.g., a focus detection zone in the case of an AF camera) into two images via a pair of separator optical systems, to be respectively formed as two separate images (right and left images) on a corresponding pair of line sensors (right and left sensors). Each line sensor includes an array of photodiodes (an array of photoelectric conversion elements). Each photodiode converts the received light into an electric charge and accumulates (integrates) the electric charge. Thereafter, the accumulated electric charges are read out of each photodiode, in order, as a picture signal (voltage). In accordance with the picture signals output from the pair of line sensors, a predetermined distance measuring process is performed to obtain data such as the amount of defocus or the object distance that is necessary for bringing the object into focus. However, in the case where this passive-type distance measuring apparatus uses a distance measuring sensor which converts the incident light into an analog picture signal, an accurate calculated distance value/amount of defocus cannot be attained by merely converting an analog picture signal output from the distance measuring sensor into a digital signal and using the digital signal in a predetermined distance measuring calculation if the brightness and/or the contrast of an object is low due to, for example, the resolving power of a low brightness portion of the digital signal being low, so that the accuracy of measurement deteriorates.
It is an object of the present invention to provide a distance measuring apparatus in which the accuracy of measurement can be increased and the time necessary for measurement can be shortened.
To achieve the object mentioned above, according to an aspect of the present invention, a distance measuring apparatus for a camera is provided, having a photometering device which can measure the brightness of an object in each of a plurality of photometering zones, including a light receiving device including distance measuring zones defined by at least a part of the photometering zones, and at least of one array of photoelectric conversion elements, wherein each of the photoelectric conversion elements converts light received thereon into an electric charge and accumulates the electric charge so that each of the accumulated electric charges is output in order from each photoelectric conversion element as an analog picture signal of the light receiving device; an A/D converter which converts the analog picture signal into digital image data; a transformation range setting device which sets a transformation range corresponding to photometering data of the photometering zones that overlap the distance measuring zones; and a logarithmic transformation device which performs logarithmic transformation on the digital image data at the transformation range to obtain sensor data.
Preferably, the distance measuring apparatus further includes an integration control device which causes the photoelectric conversion elements to commence an integration process and terminates the integration of all the photoelectric conversion elements when any one of the integral values of the photoelectric conversion elements reaches a predetermined integration completion value, so that the integral value at the termination of the integration process can be output as the analog picture signal.
The transformation range setting device determines maximum and minimum values of the photometering data of the photometering zones that overlap the distance measuring zones, and sets the transformation range in accordance with a difference between the maximum and minimum values.
Preferably, the transformation setting device reduces the transformation range as the difference between the maximum and minimum values is decreased.
Preferably, the transformation range setting device sets the transformation range while the integration process is carried out by the light receiving device.
In an embodiment, the light receiving device is arranged so that each of the distance measuring zones overlaps at least a portion of a corresponding photometering zone.
In an embodiment, the light receiving device is arranged so that each of the distance measuring zones overlaps the center portion of a corresponding photometering zone.
Preferably, distance measuring apparatus for further includes a calculation device which calculates an object distance based on the sensor data.
According to another aspect of the present invention, a camera is provided, including a photometering device which can measure the brightness of an object in a plurality of photometering zones; a light receiving device including a plurality of distance measuring zones defined by at least a part of the photometering zones, and at least one array of photoelectric conversion elements, wherein each of the photoelectric conversion elements converts light received thereon into an electric charge and accumulates the electric charge so that each of the accumulated electric charges is output in order from each photoelectric conversion element as an analog picture signal of the light receiving device; an A/D converter which performs A/D conversion of the analog picture signal to obtain digital image data; a transformation range setting device which sets a transformation range corresponding to photometering data of the photometering zones that overlap the distance measuring zones; a logarithmic transformation device which performs logarithmic transformation on the digital image data at the transformation range to obtain sensor data; and a calculation device which calculates an object distance based on the sensor data.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-39931 (filed on Feb. 17, 2000) which is expressly incorporated herein by reference in its entirety.